Aluminum borate catalyst compositions

ABSTRACT

Certain crystalline aluminum borate catalyst supports containing about 8-25 weight-percent of B2O3 are found to provide unusually stable and active catalysts for high-temperature chemical conversions, particularly exhaust gas conversion, when prepared by precalcining shaped composites of alumina and boria at temperatures between about 1,250* and 2,600*F., prior to the addition thereto of active metal or metals. Calcination at below 1,250*F. is found to yield amorphous catalysts of inferior activity, while at temperatures above 2,600*F. drastic reductions in surface area may occur.

United States Patent 7 [191 McAr'thur Dec. 24, 1974 1 ALUMINUM BORATE-CATALYST COMPOSITIONS [52] US. Cl 252/432, 252/477, 423/213.2,

423/213.5, 423/279 [51] Int. Cl B01j 11/82 [58] Field of Search 252/432,477; 423/213, 423/2132, 213.5, 279

[56] References Cited UNITED STATES PATENTS 2,118,143 5/1938 Benner et'al. 423/279 X 2,125,743 8/1938 Sweeney 252/432 X 3,331,787 7/1967 Keithet a1. 252/439 FOREIGN PATENTS OR APPLICATIONS 1,184,331 12/1964 Germany252/432 1,299,123 6/1962 France. 252/442 OTHER PUBLICATIONS LangesHandbookof Chemistry, Ninth Ed. (1956), Pub. by Handbook Publishers,Inc., Sandusky, Ohio.

Primary Examiner-Patrick P. Garvin Attorney, Agent, or Firm--Lannas S.Henderson; Richard C. Hartman; Dean Sandford [57] ABSTRACT Certaincrystalline aluminum borate catalyst supports containing about 8-25weight-percent of B 0 are found to provide unusually stable and activecatalysts for high-temperature chemical conversions, particularlyexhaust gas conversion, when prepared by precalcining shaped compositesof alumina and boria at temperatures between about l,250 and 2,600F.,prior to the addition thereto of active metal or metals. Calcination atbelow 1,250F. is found to yield amorphous catalysts of inferioractivity, while at temperatures above 2,600F. drastic reductions insurface area may occur.

15 Claims, No Drawings Thisapplication is a continuation-in-part ofapplication Ser. No. 269,544, filed July 7, I972, now abandoned.

BACKGROUND AND SUMMARY OF lNVENTlO N surface area, thermal andmechanical stability, and

suitably inert chemical properties. All of these characteristics of thesupport are interrelated and contribute in an often unpredictable mannertothe ultimate activ ity of the final catalystin its intended use. Mucheffort has been devoted in recent years to the finding of a supportmaterial which will withstand the severe mechanical and thermal stressesencountered in catalytic converters for the conversion of nitrogenoxides, carbon monoxide, and unburned hydrocarbonsin automobile exhaustgases. Some materials, e.g., alpha alumina, are suitably inert andstable, but in general do not give a final catalyst having thevolumetric activity that can be obtained from the same quantity ofactive metal or metals supported on other less stable supports such asgamma alumina. An optimum combinationof activity and stability has beendifficult to achieve.

Aluminaboria catalyst composites are known in the art, and inparticularwere extensively investigated at one time in the catalytic cracking art.However it was in general considered desirable to retain a substantialsurface area, above about 150 m lg in the final catalyst composite,'andfor this reason it was the practice to ca]- cine such catalysts atrelatively low temperatures, below about 1,200F., whichare below thetemperature required for the formation of crystalline aluminum borates.At the other extreme, US. Pat. No. 3,l72,866 discloses catalyst supportsprepared by calcining alumina-boria mixtures containing less than 5weight-percent boria at temperatures of l,6001,800C (2,912 3272F.),under which conditions the boria is apparently sublimed out of thecomposite, and a final alpha alumina support having a surface area below0.5 m /g is produced.

It has now been found that for purposes of producing a catalyst ofmaximum activity and stability for high temperature, vapor phaseconversions such as exhaust gas conversions, a much superior support isproduced by calcining certain aluminaboria composites within thetemperature range of about l,250 2,600F. Calcination within this rangeappears to produce a definite crystalline phase of 9AI O 28 and also inmost cases a crystalline phase of 2Al O .B O Although calthe specifiedrange can produce supports of adequate stabilityfor some purposes, itappears that within the range of about l,250 2,600F., an optimumcombination of crystallinity porosity, surface area, and/or chemicalproperties is produced, such that a distinct maximum activity isachieved from active metals supported on such supports. Also, suchcatalysts exhibit excellent thermal and mechanical stability up totemperatures of about 2,500 T 3 ,000F., depending mainly upon the typeof active metals present. They are also cining such composites attemperatures below or above highly resistant to shrinkage attemperatures up to .at least about 2,500F.

DETAlLED DESCRlPTlON Suitable alumina starting materials for thesupports of this invention may comprise any one or more of the so-calledtransition" aluminas. including species now commonly identified as chi,delta, eta, gamma, kappa, and theta aluminas. The various hydratedaluminas such as boehmite, gibbsite and bayerite may also be uti lized.Alpha alumina may also be utilized in applications not requiring a highsurface area. The preferred aluminas are the hydrated and/or transitionforms having a'specific surface area in the range of about I50 500 m /g.

The boria component of the support may be added as powdered B 0 or as athermally decomposable precursorthereof such as orthoboric acid,tetraboric acid,

metaboric acid, ammonium pentaborate, ammoniumtetraborate, variousorganic compounds of boron such as the boric acid esters, alkyl boranesand the like. The preferred B 0 source is ordinary orthoboric acid, HThe proportion of boron compound employed should be adjusted to'providea finished catalyst supportwherein the weight ratio of lip /A1 0 isbetween about 8/92 and 25/75, preferably between about 10/90 and 20/80.If the final composition contains more than 25 weight-percent B 0 aliquid phase will be formed at calcination or conversion temperaturesabove 470C. '(878F.), with resultant fluxing and loss of surface areaand porosity (Nature, vol. 195, July 7, 1962, pages 69-70). A liquidphase is also formed at temperatures above l,035C (1,895F.) if more than14 weightpercent of B 0 is present, but in the B 0 concentration rangeof 14-25 percent, this liquid phase is not necessarily detrimental. Aminimum of about 8 weightpercent B 0 appears to be required to achieveadequate thermal stability.

It should be understood that, unless otherwise specified, when boroncontents or ratios are expressed herein as B 0 total boron content isintended, includ ing boron present as aluminum borates and as free B203.

Conventional compounding procedures may be em- 'ployed in compositingthe two materials. It is necessary to provide an intimate admixture ofthe finely divided materials such as may be achieved by grinding,mulling, or ball milling the dry powders together, following which themixture is shaped into a porous, selfsupporting aggregate, as bytableting, prilling, extruding, casting or other well known techniquesto form cylindrical pellets or extrudates, spheres or other granularforms ranging in sizefrom about l/32-inch up to about -inch. Forprilling, extruding, or casting, the powdered mixture is ordinarilywetted with sufficient water or other liquid to form a suitable plastic.or flowable mixture, while tableting is ordinarily performed bycompressing the slightly moist but sensibly dry powdered mixture intosuitable tableting dies.

' Instead of initially dry mixing the alumina and the boron compound,the powdered alumina can be homogenized into an aqueous or other solventsolution of boric acid to provide the proper consistency for prilling,spray drying, extruding, casting, coating or the like. Also, aluminapowder can be impregnated with aqueous or other solvent solutions ofboric acid and then calcined to form an alumina boria powder which canthen be formed into any desired shape prior to the high temperaturecalcination to transform the alumina-boria,

to aluminum borate. A hydrous alumina gel. prepared by'any of the manymethods known in the art. can be peptized by the addition of boric acidin the desired amount, and the peptized gel can then be spray-dried byconventional methods to form an intimate aluminaboria mixture which canbe subsequently transformed into a shaped aluminum borate. Thesemethods, and other equivalent methods which give extremely intimateadmixture, are preferred in that they permit the final calcination to beca'rriedout at temperatures andmoved by combustion to give a monolithicbody traversed by suitable 1/32 /2-inch diameter channels for fluid flowfrom one face of the monolithto the opposite face. Other conventionalmethods for fabricating monolithic structures may also be utilized.

- Another form of monolithic support can be prepared by depositing athin layer of the alumina-boric acid slurry (in water or other solvent)over the surfaces of a preformed monolith composed of inert,low-surfacearea materials such as alpha alumina or cordierite, which inthemselves possess insufficient surface area and/or porosity forcatalytic purposes. Several such monolithic supports are commerciallyavailable, notably those composed of cordierite or spodumene in the formof corrugated septa consolidated together in layers or rolls to providea multiplicity of parallel channels from about l/32-inch to A-inch indiameter traversing the structure. To render these monoliths suitablefor use herein it is desirable to coat the-channel surfaces (externaland internal) thereof with a layer of the alumina-boria compositeranging in thickness from about 0.0005 to 0.01 cm. This may beconveniently achieved by immersing the monolith in a water or glycerolsolution of boric acid or other soluble boron compound in which thealumina component is dispersed to give a viscous slurry.

All of'the above support forms comprise, after drying at temperaturesof, e.g., 200 600F., a shaped, po-

ro'us, cohesive aggregate of finely divided alumina and boria or boriaprecursor. The shaping into a porous, co hesive aggregate (whethergranular, monolithic, or membranous) preferably takes place prior to thecritical calcinationstep. For purposes of this invention the termaggregate may be defined a cohesive mass measuring at least about 0.0005cm in at least one dimension. A cohesive aggregate is defined as onewhich, after calcination, retains its shape after boiling in water for10 minutes. The porosity of the dried aggregate prior to calciningshould be at least about 0.1 ml/g.

Minor proportions of other conventional refractory oxide supportmaterials may also be admixed with the alumina-boria composite prior tothe final shaping operation. Examples of such materials include silica,magnesia, zirconia, titania, and the like.

After drying, the shaped support is then subjected to the criticalcalcination step, as by heating in air or other gases for about 148,preferably l-12 hours at temperatures between about 1,250 and 2,600F.,preferably about 1,450 2,300F. The operation may be carried -out inconventional manner as, e.g., in a rotary kiln,

fired oven, or by passing hot gases through a fixed bed of thesupportflt is preferable to raise the support material to the finalcalcining temperature over a period of about 1 to 5 hours. The overallseverity of the calcination should be controlled to produce in the firstinstance a substantial, X-ray-detectable phase of crystalline 9Al O .2BO corresponding substantially to the following diffraction pattern:

This phase is normally produced in the form of well defined crystalliteshaving an average size of about 250A., which are easily detectable byX-ray diffraction analysis. Preferred forms of the support will alsocomprise a relatively minor phase, believed to be 2A1- 0 E 0 in the formof smaller crystallites having an average size of about 1-30 A., andwhich are usually not as readily detectable by X-ray analysis. Thisphase (which is believed to enhance mechanical and thermal stability)exhibits the following major spacings:

Table2 dA l/l dA 1/1 dA 1/1,- dA 1/1 15.4 60 3.33 2.054 60 1.638 80 7.4440 3.29 60 2.038 40 1.552 6.56 60 2.93 60 1.981 40 1.531 60 5.29 1002.76 80, 1.949 60 1.488 100 5.23 100 2.65 100 1.912 60 1.470 80 4.90 1002.60 100 1.812 80 1.424 so 4.27 80 2.44 100 1.783 60 3.74 40 2.38 401.776 80 3.65 40 2.21 80 1.736 20 3.58 60 2.134 100 1.712 40 3.55 802.122 60 1.679 20 3.36. 80 2.085 so 1.664 60 I The size of thecrystallites produced in the calcination is the primary parametergoverning critical functional aspects of the support, such as mechanicaland thermal stability, porosity, pore size distribution, and surfacearea. Calcination temperatures in the high ranges tend to produce largecrystallites with resultant reduction in surface area and increase inaverage pore size. Conversely, the lower temperature ranges tend to givesmaller crystallites, higher surface areas and smaller pores. Theseparameters of pore size and surface area can thus be made to varyconsiderably, depending upon the intended use of the catalyst. In manycatalytic processes extremely high surface areas and pore volumes arenot required, or may even be detrimental. ln any case, it is normallydesirable to preserve at least about 1, preferablyat least about 5, mlgm of surface area, and at least about 0.1, preferably at least about0.2, ml/g of total porosity.

When the ultimate catalyst is intended for use in the present in thesupport when the active metal compo nent is added. Free B 0 melts atabout 860F. and develops a substantial vapor pressure at temperaturesabove about 1,200F. Hence, during calcination following the addition ofactive metal salts, and/or during subsequent use of the catalyst at hightemperatures, any free boria becomes very mobile and active as liquidand/or vapor, and tends to combine with and deactivate most of thecommon transitional metal catalyst components. Also, if any water ispresent, volatile metaboric acid may be formed, which becomes verycorrosive to ferrous metals at elevated temperatures, as is molten B 0itself. In contrast to the hydrothermal instability of B 0 the compounds9Al O .2B O and 2Al O .B O appear to be hydrothermally stable up totemperatures of at least about 3,540 F. and 1,895F., respectively.

The maximum boria content weight-percent) specified herein correspondssubstantially to the com- ,pound 2Al O .B O (the 2:1 compound). Theconcentration of 13.3 weight'percent B 0 corresponds to the compound 9A|O .2B O (the 9:2 compound). The intermediate concentrations correspondto mixtures of the 2:1 and 9:2 compounds. Boria contents below 13:3percent correspond to mixtures of the 9:2

compound and free A1 0 It would hence appear that in theory no freeboria should be present in the final calcined supports. However,depending upon the intimacy of admixture of the initial alumina andboria components, the temperature and time'iof calcination and perhapsother factors, some free boria is usually present in the calcinedcomposites-Also, at calcination temperatures above about 1035C.(1895"F), the 2:1

compound breaks down to form free boria and the 9:2

including Table 3 Boron Boron removal. I Content of total SampleTreatment Wt 7r initially present 1 None 6.91 2 Steaming at F. for 6.752.3 16 hours 3 Calcination 5.99 13.3

at 2200F for 1 hour 4 Leaching with boiling 6.47 6.4

water for 2 hours 5 Boiling water leaching 5.92 14.3

for 2 hours NH OH leaching for 1 hour Leaching with boiling water and/orwith warm, concentrated NH,OH solutions appear to be the most effectivetreatments. The effectiveness of calcination at 2,200F. (Sample 3) isnot readily apparent, for at that temperature some of the 2:1 compoundwas undoubtedly converted to the 9:2 compound and free boria. Upongradual cooling however, this free boria would in theory combine with aportion of the 9:2 compound to reform the 2:1 compound.

To illustrate the utilitarian effect of removing free boria, twocomparisons were made on exhaust gas conversion (oxidation), using inone experiment a catalyst (A) containing 24 weight-percent B 0 in thesupport and from which free boria had not been removed, and in the othera catalyst (B) containing the same active metals, but supported on abase which had been leached in boiling water to reduce the B 0 contentto It is thus apparent that removing free boria from catalyst B resultedin at least about a 200 temperature advantage for hydrocarbon conversionand a 300 advantage for CO conversion.

By virtue of the foregoing methods for removing free B 0 it is feasibleto employ initially a substantial excess of boria or boria precursor,over the proportion desired in the final support, whereby essentiallyall of the alumina can be reacted at shorter calcination times and/orlower temperatures. In many cases it is desirable to provide a supportcontaining substantially no free A1 0 in order to prevent the formationduring subsequent use of relatively inactive aluminates or spinels ofthe active metal or metals supported thereon. By the techniquesdescribed above it is entirely feasible to prepare supports containingless than about 1 weightpercent of free B and less than about 5weightpercent of free Al O However, in utilizing this excessboriatechnique, not more than about 40 weightpercent, preferably less thanabout 30 weight-percent of boria should be employed in the initialalumina-boria mixture. If too large an excess of boria is utilized, suchthat more than about -20 weight-percent of free B 0 remains in thecalcined aggregates, such aggregates will tend to disintegrate into apowder or slurry upon subsequent removal of the excess free boria (seeU.S. Pat. No. 3,080,242). An important attribute of the calcinedsupports prepared as herein prescribed is their mechanical strength,which normally exceeds that corresponding to a crushing strength of.pounds for /5 X 4; inch extrudate pellets.

Following clacination and removal of free boria, the support may beimpregnated in conventional manner with a solution or solutions of thedesired catalytic metal salt or salts. Any one or more of thetransitional metals or compounds thereof may be utilized, the morewidely used of such being the metals of Groups 18, 11B, VB, VlB, VllB,and VIII of the Periodic Table, and their oxides and sulfides. Exemplarymetals are zinc, cadmium, copper, siler, chromium, molybdenum, tungsten,manganese, rhenium, iron, cobalt, nickel, ruthenium, rhodium, palladium,osmium, iridium, and platinum. ln exhaust gas conversion catalysts, themore commonly used metals are copper, chromium, molybdenum, manganese,iron, cobalt, nickel, ruthenium, palladium and platinum, or combinationsthereof. The iron group metals, and the metals of Groups 1B, [1B, VB,VIB, and VllB are normally employed in proportions ranging between about3 percent and 30 percent, preferably about 6-20 percent by weight, basedon the corresponding oxides. The Group VIII noble metals such aspalladium and platinum are normally employed in smaller proportionsofabout 0.05 2 percent by weight. I

The salts employed for impregnation are preferably those which arethermally decomposable to give the corresponding metal oxides and/orsulfides. Preferred salts are the nitrates, acetates, chlorides,oxalates, sulfates and the like. Following impregnation, the finishedcatalysts are produced by draining, drying and if desired, calcining attemperatures of, e.g., 500 to 1,000F. In the final catalyst the activemetal or metals may appear in the free form, as oxides or sulfides, orany other active form.

A preferred class of exhaust gas conversion catalysts comprises about5-10 percent by weight of copper as CuO and about 5-15 weight-percent ofiron, cobalt and/or nickel, as Fe O C0 0, or NiO. These metals,especially copper and iron, are apt to bring about severe shrinkage ofconventional transition alumina supports at exhaust gas conversiontemperatures. But when employed on the supports of this invention, theshrinkage is substantially nil.

Another preferred. class of exhaust gas conversion catalysts comprisesabout 0.05 1.0 weight-percent of one or more .Group Vlllnoble metals,particularly platinum and/or palladium, together if desired with 1% to10% of one or more of the metals, V, Cr, Mn, Co, Ni, Cu, and Zn.

USE OF CATALYSTS Catalysts based on the supports ofthis invention may beemployed to catalyze any chemical conversion in which supported activemetals or metal compounds may advantageously be utilized. However, dueto the remarkable thermal and hydrothermal stability of the supports,catalysts based thereon are most advantageously utilized in chemicalconversions carried out at elevated temperatures of e.g., 600 3,000F.,and even more advantageously in processes requiring temperatures in therange of about 900 3,000F.

Several general rules can be followed in selecting an optimum supportfor the particular reaction concerned. Firstly, for reactions carriedout at above about 1,900F., it is preferred to utilize a supportcontaining less than about 15 weight-percent, preferably less than 13weight-percent of B 0 so as to eliminate or minimize the formation ofliquid B 0 resulting from the conversion of the 2:1 aluminum borate-tothe 9:2 compound. For reactions carried out at below about. 1,900F., itis preferred to utilize supports containing about 13-25 weight-percentof B 0 so as to obtain maximum mechanical stability and surface area. Itis also a general though not infallible rule that reactions carried outat very high temperatures with all reactants in the vapor phase requireless porosity and surface area in the support than do reactions carriedout at relatively low temperatures and/or with one or more of thereactants in the liquid phase. Where liquid phase reactants areinvolved, it is hence preferred to utilize supports having a porosity ofat least about 0.5 ml/g, and a surface area above about 40 m /g. Forvapor phase reactions carried out at temperatures above about 1,200F.,it is normally feasible to utilize supports having surface areas in thelow range of about l-20 m /g, and porosities in the range of about 0.20.7 ml/g. For low temperature vapor phase reactions, somewhat highersurface areas and pore volumes are generally desirable.

Another factor to be considered in selecting a suitable support is theamount and type of active metal or metals to be added thereto, and thedegree of its dispersion on the support. Obviously, where high metalloadings are desired, a primary consideration is high porosity.Generally, higher porosity is obtained at the higher calciningtemperatures. In cases where the active metal or metals are added to thesupport in such manner as to obtain a very high degree of dispersionthereon a relatively low surface area support may suffice, whereashigher surface areas may be required if the active component is nothighly dispersed. With the aid of a minimum of judiciousexperimentation, these general guidelines can be used to effectivelyarrive at optimum aluminum borate supports for the particular chemicalreaction concerned. 1

Depending to some extent upon the particular reaction involved, anyconventional catalytic contacting technique may be employed, includingfixed bed, moving bed, fluidized bed and slurry contacting procedures.Normally a fixed bed operation is preferred with the reactants beingpassed in vapor phase, liquid phase, or mixed phase through a bedofmacropellets of catalyst.

While it is obviously impossible to cite all possible chemical reactionsin which the catalysts of this invention may be utilized, some of themore important and matic hydrocarbons, hydrodesulfurization and/or hy-'drodenitrogenation of mineral oils or fractions thereof, etc.

As previously indicated, catalysts of this invention are particularlyuseful for the conversion of nitrogen,

oxides, unburned hydrocarbons and carbon monoxide in internal combustionengine exhaust gases. Exhaust gases in the exhaust manifoldnormallyattain temperatures of l,200-l ,600F., and peak temperatures indownstream catalytic converters can exceed 2,000F., particularly whenthe exhaust is rich in unburned hydrocarbons which, with the aid ofadded air, are being oxidized in the converter. At these temperaturesmost catalysts lose substantially all of their activity, usually as aresult of the formation of inactivecombinations between the activecatalyst component and the support. However, catalysts based on thesupports of this invention are found to maintain theiractivity forconverting nitrogen oxides, hydrocarbons and carbon monoxide attemperatures in excess of 2,000F. A particularly suitable exhaust gasconversion catalyst comprises about -l0 weight-percent of copper as CuOand about 5-l5 weight-percent of nickel as NiO.

The hydrogenation of carbon oxides (methanation) to produce methane isgenerally carried out at temperatures ranging between about 600F. and1,500F. and pressures between about 100 and L500 psig. The reaction isextremely exothermic, and much difficulty has been encountered incontrolling temperature rise in the reactor. One widely used techniqueinvolves the recycle oflarge volumes of product gases (mainly methane)merely to serve as a heat sink, thus adding greatly to operating costs.Catalysts previously available for this process have been found tobecome substantially deactivated if temperatures in excess of about1,l00 l,200 are reached during methanation, to the extent that they willnot initiate the reaction at temperatures below about 1,200F. Someactivity at temperatures above l,200F., is usually retained, but, atthese high temperatures the equilibrium for methanation is unfavorable;it is therefore a practical necessity to carry out a substantial portionof the methanation at temperatures below 1200F. However, it is alsodesirable to have a catalyst which does not place a ceiling" on thepermissible exothermic temperature rise; by removing this ceiling theneed for expensive temperature control measures is reduced oreliminated.

It will hence be apparent that in methanationa catalyst active over-theentire temperature range of about 500 l,500F., and especially attemperatures above l,200F., is highly desirable. Also, since steam isproduced during methanation, a hydrothermally stable catalyst is alsorequired. The catalysts of this invention appear to be ideally suited tothese requirements. Metals active methanation catalyst include primarilythe Group VIII metals, and particularly nickel, or nickel promoted withcerium. Preferred methantion catalysts for use herein comprise about5-40 weight-percent of nickel as NiO supported on the aluminum boratebases of this invention.

Steam reforming of methane, or C C paraffins, to produce hydrogen is theendothermic reverse of the methanation reaction, and is normally carriedout at temperatures ranging between about 1,500" and 2,000F. The hightemperatures and presence of steam again present a problem in activitymaintenance, since the same type of catalysts used for methanation areordinarily used for steam reforming. Here again the catalysts ofthisinvention find particular utility by virtue of their hydrothermalstability and activity maintenance.

Dehydrocyclization reactions are normally carried out at temperatures ofabout 850 l,l50F. and pressures of about 0-50 psig. Primary feedstockscomprise paraffin hydrocarbons, preferably normal paraffins,

having at least six carbon atoms, e.g., n-hexane, n-

heptane, n-octane and the like, the corresponding products comprisingmainly benzene, toluene, xylene and the like. Active catalyticcomponents for dehydrocyclization comprise between about 0.1 20weightpercent of one or more hydrogenating metals, preferably the metalsof Group VIB and/or VIII, e.g., nickel, palladium, platinum, molybdenum,etc. and the oxides and sulfides thereof.

Dehydrogenation reactions are carried out under the same generalconditions decribed above for dehydrocyclization, and the same type ofactive catalytic components are utilized. Substantially any paraffinicor alkyl aromatic hydrocarbon may be dehydrogenated to correspondingunsaturated compounds. For example ethane may be converted to ethylene,propane to propylene, butane to butene or butadiene-, cyclohexane tobenzene, methyl cyclohexane to toluene, ethylbenzene to styrene, etc.

Naphtha reforming operations are preferably carried out at temperaturesof about 800 l,000F., hydrogen pressures ranging between about and 600psig, and liquid hourly space velocities of about 0.5 5. Preferredfeedstocks comprise straight run and/or cracked naphthas boiling in therange of about 200 450F.,

while the preferred active catalytic components comprise Group VIIInoble metals, particularly platinum, employed in amounts of about 0.l -2weight percent.

In catalytic hydrodealkylation, the objective is to effect scissionofparaffinic side chains from aromatic rings without substantiallyhydrogenating the ring structure. To accomplish this objective,relatively high temperatures in the range of about 800 l,200 areemployed at moderate hydrogen pressures of about 300 1000 psig.Operative catalytic components comprise about 0.1 4 20 weight-percent ofone or more hy- EXAMPLES l6 Boehrnite alumina powder was ball milled anddry mulled with sufficient powdered boric acid to provide a 20% B 80% AIO composite, and the homogeneous powder was then mixed with sufficientdilute ni- 1s tric acid to provide an extrudable plastic mass. Themixture was then extruded i'nto fia-inch diameter pellets and dried.Separate portions thereof were then calcined at various temperatures asindicated in Table l, for 24 hours. The samples calcined at 1,200 and1,400F. were amorphous, while those calcined at the higher temperatureswere highly crystalline. Each of the calcined samples were thenimpregnated with an aqueous solution of copper nitrate and cobaltnitrate to provide about 4% copper as CuO and 12% cobalt as C0 0 in thefinal catalyst. After draining and drying at l 10C., the catalysts weretested for nitric oxide conversion activity and selectivity, using. asthe feed a synthetic exhaust gas having the following composition:

Mole 71 ('0 L0 H 0.33 cm, 0.10 NO 0.08 H O 10.0 Air (0 L4] (0.3)

The test procedure consisted in passing the feed gas through thecatalyst bed at a gaseous hourly space velocity of 23,000, measuring NOconversion at about l,000F. (which generally gives 100% conversion),then at successively lower temperatures so as to bracket the 50%conversion temperature and obtain temperature coefficients. From thisthe 50% conversion temperatures were calculated, based on the firstorderrate equation. Selectivityof conversion to nitrogen was determined atl,250F. (0Selectivity" is the percent of NO converted which wasconverted to N rather than to NH The latter is undesirable because inmost catalytic exhaust gas converters, any ammonia formed is ultimatelyoxidized back to NO and emitted to the atmosphere as a pollutant.) Theresults of the test runs were as follows:

It is readily apparent that catalysts 36. based on supports which werecalcined at temperatures within the preferred range of the invention,were substantially more active and in most cases more selective thancatalysts l and 2, based on supports calcined at temperatures below thepreferred range. It should not be con cluded however that thetemperature range of 1,250 1,400F. is inherently inoperable; as will beshown hereinafter this temperature range is effective when preferredsupport preparation techniques are utilized.

EXAMPLES 7-10 Four additional catalysts were prepared as described inExamples l-6, with the exception that the Al O;,/- B 0 weight-ratio was86/14 instead of /20. Upon testing as describedin Examples l6, thefollowing results were obtained:

Table 6 Support Conversion of NO Precalcination Temp, F. for 50%Selectivity Catalyst Temp., F. Conversion to N Z (amorphous) 8 L400 860'48 (amorphous) 9 L600 675 94 (crystalline) 10 1.800 672 94(crystalline) Here again, the superiority of the crystalline supports ofthis invention is readily apparent.

EXAMPLES ll -16 Six additional catalysts were prepared as described inExamples l6, except that the catalyst loading was 8% copper as CuO and8% cobalt as C0 0 and in two cases gibbsite alumina was used instead ofboehmite.

Gibbsite alumina thus appears to be somewhat more effective thanboehmite alumina in the catalyst supports of this invention.

EXAMPLE 17 mina powder were mixed together in a blender to form a milk.Stirringwas continued for anadditional 15 min-- utes, whereupon thetemperature of the mixture increased to -175F., and its consistency wasthat of a fluffy paste. An additional 52 g of boehmite were added to thepaste and the mixture was hand stirred with a spatula to form ahomogeneous thick heavy paste. The paste was injected into rubbercasting mats (forming molds), and the filled mats were then placed in adrying oven and dried in air at a temperature of 1 C for 3 hours.Following the drying step, the pellets were removed from the castingmats with an ejection punch. The cast pellets, comprising '20weight-percent B 0 were hard, strong, and exhibited good form.Individual samples of the pellets were then given various aircalcination treatments with the following results:

in support A, approximately 30 percent of the pore volume is in pores ofgreater than 100 A. diameter, whereas in support B almost 100 percent ofthe pore volume is in pores of diameter greater than 100 A.

EXAMPLE 18 About 250 g of ground Mallinckrodt analytical reagent gradeboric acid powder and 660 g of Kaiser boehmite alumina powder were mixedtogether and dry mulled for 30 minutes. Mulling was then continued witha steady slow addition of dilute nitric acid solution (pH 2.0). The timeof wet mulling was 45 minutes, and 564 ml of nitric acid solution wasused. The finished mull was placed in a barrel-plunger type extruder andextruded through a %l11Ch diameter die at a pressure of 800 psig. Theextrudates were airdried at room temperature for 16 hours, and thenbroken up into the desired lengths lto einch). lndividual samples of theextrudates were then given various air calcination treatments, with thefollowing results:

Table 9 Surface 1 Sample Temp., Time Hrs Amorphous Crystalline EXAMPLE19 A suitable monolithic catalyst support was prepared as follows:

To 250 ml ofglycerol was added over a minute period 100 g of Kaiserboehmite alumina while stirring and heating to 145C., at whichtemperature the slurry was aged for 1 hour. An additional 28 g ofboehmite was added, followed by aging-an additional minutes. Then 33.8 gof granular boric acid was added, whereupon the slurry became thinnerand the temperature dropped to 125C. After aging for 35 minutes, anadditional 15 g of boric acid was added, followed by aging an additional65 'rninuteslThe slurry then appeared to be too viscous, so anadditional 100 ml of glycerol was slowly added, followed by heating anadditional 60 minutes.

Next, four American Lava uncoated cordierite monolithic supports, Al SiMag 795, of the rolled corrugated type 12/8 were immersed in the slurryand soaked for 15 minutes at 135C, after which they were removed andplaced in Gooch crucibles where the excess coating was removed by vacuumstripping. 1n addition to suction below, an air jet was directed fromabove to clear the flow passages of the monolith of excess coatingmaterial. After stripping, the coated monoliths were air dried in anoven at 110C for 30 minutes, then heated in a furnace to 1,800F. over a4- hour period and calcined at that temperature for 24 hours.

The surface area of the resulting monoliths were determined by nitrogenadsorption (BET) to be 30 m /g. This monolith, when impregnated withabout 8 weightpercent NiO and 8 weight-percent CuO, provides a highlyactive and selective NO, conversion catalyst, which is stable up totemperatures of at least about 2,200F.

EXAMPLE 20 This example demonstrates that crystalline supports can beprepared at calcination temperatures below 1,400F., if a preferredcompounding procedure is employed:

About 650 g of boric acid powder were dissolved in 1700 ml of hotdistilled water, and the solution'temperature was raised to 97C. 800 gof alumina powder (boehmite) were added to the boric acid solution withcake was air-dried for 1 hour. The wet powder was then oven-dried at220F. for 1 hour and calcined in air as follows: the temperature wasincreased from 100 to 800F. over a period of 12 hours, and then heldconstant at 800F. for 2 hours, followed by a slow (-16 hours) cooling toambient temperature.

and dry-ground for 30 minutes. 500 ml of concentrated NH OH were addedto the powder and mulling was continued for 10' minutessThen 470 ml ofdistilled water were added and the mulling was continued for anadditional 125 minutes. The m'ull was then extruded through a Vsinchdiameter die at 600 psig using a pistoncylinder type extruder. Theextrusions were dried at C. for 1 Va hours in a forcedlair oven, brokenup to 16 hours, and then analyzed by X-ray diffractiorito; determinestructure and composition. The results were as follows:

Table l 1 Effect of Calcination Time at l300F. On The CrystallineStructure of Aluminum Borate Extrudates crystallization temperature.Another desirable method is to mix boric acid with a hydrous aluminageland then spray dry the peptized hydrous gel.

EXAMPLE 21 "3 Tl'llS example illustrates the preparation of a pre-'ferred methanation catalyst of this invention. 1 An aluminum boratertainch extrudate support containing about 17 weight-percent B 0 wasprepared essentially as described in Example 20, but was calcined in airat 1,800F. for 14 hours and then steamed at I000F. for 24 hours. About1,520 g of Ni(NO 6H O was dissolved in sufficient distilled water togive a total volume of 1,000 ml. This solution was then used toimpregnate l,000 ml of the support. After draining off excess solution,the impregnated extrudates were then calcined in air at temperaturesgradually increasing from 100 750F. over a l2 hour period, and held at750F. for an additional 2 hours. Analysis of the resulting catalystshowed the following properties:

into small extrudates. and calcined as follows: the temperature wasincreased from 100 l,200F. over a period of l2 hours, held constant at1.200F. for 2 hours, and then cooled slowly (-l6 hours) to ambienttemperature. The properties of the calcined extrudates were as follows:

Table 10 Properties of Alumina-Boria Extrudates Calclned ln Air atl200F.

Water Pore Volume Compacted Bulk Density X-Ray Analysis 0.65 cmlg 0.5lg/cm amorphous alumina-boria Various samples of the l,200F. calcinedextrudates were calcined in air at 1,300F. for periods of from 1 EXAMPLE22 The catalyst of Example 21 was compared for methanation activity in a6-day life test with a commercial methanation catalyst comprising about25 weightpercent nickel supported on an activated M 0 base containingabout 17 weight-percent ofa calcium alumi- -nat'e binder. The test unitconsisted ofa 96inch [.D. tube 'holding 50 ml of catalyst, giving a7-inch bed depth, with a thermocouple well extending longitudinallythrough the catalyst bed so that exothermic temperature rises (ATs) ateach inch of bed depth could be detected. With downflow of feed gas inthis apparatus, the rate of progressive catalyst deactivation ismeasured by the rapidity with which the peak AT moves downwardly throughthe catalyst bed, signifying deactivation of the catalyst upstream fromthe peak AT.

Using a feed gas comprising 38.5% CH 18.6% H 5.0% CO and 37.9% H O byvolume, and at a pressure of 300 psig and a dry gas space velocityof5,000 v/v/hr, the results were as follows:

Table 13 Results with Catalyst of Example 2l Days on Stream 1 2 3 4 5 6lnlet Temp.. F. 918 925 950 925 920 900 Catalyst Bed Temp. F.

AT First lnch ll7 l63 I75 180 l I80 AT Second Inch 38 47 35 50 60 ATThird Inch 0 O 0 0 0 0 Total AT 155 215 210 230 220 250 Results withCommercial Catalyst Days on Stream 1 2 3 4 5 6 lnlet Temp, "F. 893 915905 920 9l8 Catalyst Bed Temp. F.

AT First lnch 52 40 25 30 20 AT Second lnch I25 I15 I10 8O 70 AT Thirdlnch 0 40 55 H5 AT Fourth Inch 0 0 0 0 5 Total AT l77 I I90 210 drivento equilibrium in,the first 2 inches of catalyst bed throughout the run.The commercial catalyst however was deactivating fairly rapidly, asevidenced by the decline in activity of the second inch of the bed andthe rising activity appearing in the third and fourth inch. After about20 days of operation in this manner, the entire bed of the commercialcatalyst would be deactivated.

The following claims and their obvious equivalents are intended todefine the true scope of the invention:

1 claim:

1. A shaped, porous, cohesive aggregate consisting essentially ofcrystalline aluminum borate having a surface area between about 1 and150 m /g and a porosity of at least about 0.1 ml/gram, and wherein theweightratio of B O /Al O is between about 8/92 and 25/75, said aggregatehaving been formed by calcining a preshaped composite of alumina andboria, orboria pre- 2,600F for a sufficient time to produce saidcrystalline aluminum borate, said preshaped composite comprising betweenabout 8% and40% by dry weight of B 0 equivalent.-

2. A shaped aggregate as'defined in claim 1 wherein the weight-ratio ofB O /Al O is between about 10/90 and 20/80.

3. A shaped aggregate as defined in claim 1, said aggregate having beencalcinedat temperatures between about l,450 and 2300?. V g

4. A shaped aggregate as defined in claim 3 wherein the weight-ratio ofB O /Al O is between about 10/90 and 20/ 80.

5. A shaped aggregate as defined in claim 1, having a surface areabetween about 5 and 150 m /g.

18 6. A shaped aggregate as defined in claim 5 wherein the weight-ratioof B O /AI O is between about 10/90 and 20/80.

7. A shaped aggregate as defined in claim 6, said ag gregate having beencalcined at temperatures between about 1,450 and 2,300F.

8. A shaped aggregate as defined in claim 1, in the form of l/32 /2 inchgranules.

9. A shaped aggregate as defined in claim 1, in the form ofa monolithicstructure traversed by channels of about l/32 inch in diameter. I

10. A shaped aggregate as defined in claim 1, in the form of amembranous coating supported on an inert monolithic structure traversedby channels of about l/32 A inch in diameter.

11. A shaped aggregate as defined in claim 1 containing less than about1 weight-percent of free B 0 12. A shaped aggregate as defined in claim1 containing less than about 5 weight-percent of free A1 0 13. A shapedaggregate as defined in claim 1, having a surface area between about 5and m /g and a porosity between about 0.2 and 0.8 ml/g.

14. A shaped aggregate as defined in claim 1, said ag' gregatecontaining a minor proportion of free B 0 and having been leached with areagent selected from the' class consisting of hot water and aqueousammonia, for

a sufficient time to extract a substantial portion of said 2,600F, theproportions of alumina and boric acid in said suspension being adjustedto provide an aluminum borate coating on said monolith containingbetween about 8% and 40% by dry weight of B 0

1. A SHAPED, POROUS, COHESIVE AGGREGATE CONSISTING ESSENTIALLY OFCRYSTALLINE ALUMINUM BORATE HAVING A SURFACE AREA BETWEEN ABOUT 1 AND150 M2/G AND A POROSITY OF AT LEAST ABOUT 0.1 ML/GRAM, AND WHEREIN THEWEIGHT-RATIO OF B2O3/AL2O3 IS BETWEEN ABOUT 8/92 AND 25/75, SAIDAGGREGATE HAVING BEEN FORMED BY CALCINING A PRECURSOR, AT TEMPERATURESBETWEEN ABOUT BORIA, OR BORIA PRECURSOR, AT TEMPERATURES BETWEEN ABOUT1,250* AND 2,600*F FOR A SUFFICIENT TIME TO PRODUCE SAID CRYSTALLINEALUMINUM BORATE, SAID PRESHAPED COMPOSITE COMPRISING BETWEEN ABOUT 8%AND 40% BY DRY WEIGHT OF B2O3 EQUIVALENT.
 2. A shaped aggregate asdefined in claim 1 wherein the weight-ratio of B2O3/Al2O3 is betweenabout 10/90 and 20/80.
 3. A shaped aggregate as defined in claim 1, saidaggregate having been calcined at temperatures between about 1,450* and2, 300*F.
 4. A shaped aggregate as defined in claim 3 wherein theweight-ratio of B2O3/Al2O3 is between about 10/90 and 20/80.
 5. A shapedaggregate as defined in claim 1, having a surface area between about 5and 150 m2/g.
 6. A shaped aggregate as defined in claim 5 wherein theweight-ratio of B2O3/Al2O3 is between about 10/90 and 20/80.
 7. A shapedaggregate as defined in claim 6, said aggregate having been calcined attemperatures between about 1,450* and 2, 300*F.
 8. A shaped aggregate asdefined in claim 1, in the form of 1/32 - 1/2 inch granules.
 9. A shapedaggregate as defined in claim 1, in the form of a monolithic structuretraversed by channels of about 1/32 - 1/4 inch in diameter.
 10. A shapedaggregate as defined in claim 1, in the form of a membranous coatingsupported on an inert monolithic structure traversed by channels ofabout 1/32 - 1/4 inch in diameter.
 11. A shaped aggregate as defined inclaim 1 containing less than about 1 weight-percent of free B2O3.
 12. Ashaped aggregate as defined in claim 1 containing less than about 5weight-percent of free Al2O3.
 13. A shaped aggregate as defined in claim1, having a surface area between about 5 and 150 m2/g and a porositybetween about 0.2 and 0.8 ml/g.
 14. A shaped aggregate as defined inclaim 1, said aggregate containing a minor proportion of free B2O3 andhaving been leached with a reagent selected from the class consisting ofhot water and aqueous ammonia, for a sufficient time to extract asubstantial portion of said free B2O3 without essentially altering theshape of said aggregate.
 15. A method for the manufacture of a coatedmonolithic catalyst support, which comprises coating an inert monolithicstructure traversed by channels of about 1/52 - 1/4 inch in diameterwith a suspension of alumina in a glycerol solution of boric acid, andthereafter draining, drying and calcining the coated structure at atemperature between about 1,250* and 2,600*F, the proportions of aluminaand boric acid in said suspension being adjusted to provide an aluminumborate coating on said monolith containing between about 8% and 40% bydry weight of B2O3.